An engine of a vehicle combusts a mixture of air inflowing from outside and a fuel with an appropriate ratio to generate a power.
In a process of generating the power by driving the engine, external air for the combustion must be appropriately supplied to obtain a desired output and combustion efficiency. For this, a turbocharger as a device for turbocharging the air for the combustion to increase the combustion efficiency of the engine is used.
In general, a turbocharger is a device that rotates a turbine by using pressure of exhaust gas discharged from an engine and thereby increases output of the engine by supplying high-pressure air to a combustion chamber by using rotational force thereof. The turbocharger is applied to most diesel engines and has also recently been applied to gasoline engines.
As another example of an intake boost device, an electric supercharger using a motor to drive a compressor to compress external air has been used. Since the electric supercharger is driven by a battery, there is little boost, and it mainly supplies supercharged air to the cylinder in a low speed and low load region.
In general, the turbocharger (hereinafter referred to as ‘a mechanical turbocharger’) operated by the exhaust gas has low responsiveness, and it is difficult to realize a high compression ratio because of a magnitude of a back pressure. Since the turbocharger is exposed to an exhaust gas of high temperature (about, 700° C.), a design cost of turbocharger surrounding components increases.
Nitrogen oxide (nitrous oxide; NOx) within an exhaust gas exhausted from the engine causes acid rain, stimulates eyes and respiratory organs, and kills plants. NOx is regulated as an atmospheric pollution source and there has been an effort to lessen exhaust of NOx.
An exhaust gas recirculation (EGR) system has been provided to a vehicle for reducing noxious exhaust gas. Generally, NOx is increased in a case where an air-fuel ratio of an air-fuel mixture is high, which is necessary for sufficient combustion. Thus, the exhaust gas recirculation system mixes an exhaust gas from an engine to the air-fuel mixture, for example 5-20%, thereby reducing the amount of oxygen in the air-fuel mixture and obstructing from combustion, and so lessening generation of NOx.
The general exhaust gas recirculation system recirculates the exhaust gas exhausted through an exhaust manifold from the cylinder of the engine and flowing to the exhaust line into the cylinder of the engine through the recirculation line, and an EGR valve is mounted on the recirculation line to control an EGR rate.
The exhaust gas recirculation system may be classified into a low pressure EGR (LP EGR: low pressure exhausted gas recirculation) system and a high pressure EGR (HP EGR: high pressure exhausted gas recirculation) system.
In the conventional exhaust gas recirculation system, the exhaust gas is recirculated through the EGR line that is branched from the exhaust line flowing the exhaust gas and is joined into the intake line. In this case, in the EGR line, an EGR cooler cooling the recirculated exhaust gas and an EGR valve controlling the recirculated exhaust gas amount are installed.
Among the conventional exhaust gas recirculation apparatus, in the high pressure EGR system as a method supplying the recirculation gas (the EGR gas) to the intake manifold by using high pressure of the exhaust manifold, since a difference pressure is low between the exhaust manifold and the intake manifold in a driving region (e.g., the supercharged air is supplied by the turbocharger or the electric supercharger) that the pressure of the intake manifold increases, it is difficult to supply the recirculation gas and the driving region that the recirculation gas is supplied is limited.
In the low pressure EGR system as a method supplying the recirculation gas to the intake line of a compressor upper stream of the turbocharger from the exhaust line of the exhaust gas purification device lower stream, when the recirculation gas is supplied, since a fresh air supply amount decreases, the driving region that the recirculation gas is supplied is limited. There are problems that a control logic for supplying the recirculation gas is complicated and a manufacturing cost increases.
As above-described, in conventional, since the exhaust gas recirculation device must be additionally provided for the exhaust gas recirculation, the manufacturing cost of the vehicle increases and a design freedom of the engine room inside is poor.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.